Fish meal is a fishery by-product consisting essentially of process scrap from the filleting operation or from whole fish. Fish meal can be produced by a dry process wherein waste from cod, halibut, and haddock heads is disintegrated and dried.
A wet process also exists for the production of fish meal. FIG. 1 illustrates a known process for producing fish meal from the carcasses of processed pollock. In this known process, the processed carcasses 240 are cooked in a steam cooker 250 prior to delivery to a screw press 260 that separates the cooked carcasses into a press cake 262 rich in solids and a press fluid 264 rich in fluids. The press cake is delivered to a dryer 320 where water 322 is removed and fish meal 324 is recovered. The press fluid is processed through a decanter 280 which separates the press fluid into sludge 282 rich in solids and a fluids rich component 284. The sludge is delivered to the dryer where water is removed and fish meal recovered. The fluids rich component is delivered to a centrifuge 300 that is used to separate fish oil 302 from the fluids rich stream and provide a solids cake 304 and a fluid stream 306. An evaporator 310 is used to remove water 312 from the fluid stream from the centrifuge and concentrate the fish protein solids 314 in the fluid stream from the centrifuge. The concentrated fish protein solids are then delivered to the dryer for removal of the residual water. Each of the successive separations performed by the decanter, centrifuge, and evaporator recovers a portion of the fish protein solids that the previous separation process was unable to isolate and recover.
The increasing worldwide demand for processed fish products has resulted in the production of larger amounts of fishery by-products which are available to be processed into fish meal. In an effort to recover the fish protein solids present in these raw materials and convert them into fish meal, existing fish meal production facilities are often pushed to capacity or over capacity. A typical raw material stream includes 70-80% water in which the fish protein solids are either dissolved or suspended. During the production of fish meal, this water must be treated and the fish protein solids separated therefrom. In existing fish meal processing plants, it is often the capacity of the separation operations, such as the decanter, centrifuge, evaporator or dryer that limits the volume of water that can be handled by the system. While it may be possible to upgrade the existing equipment by replacing it with larger capacity equipment, such upgrades do not come without an economic cost. A similar dilemma is faced in the building and design of new fish meal production facilities. The need for larger capacity separation equipment naturally makes the return on investment lower.
When the raw material originates from fish that were refrigerated in salt water, steps must be taken to remove a portion of the salt so that the recovered fish meal product has an overall salt content that meets industry standards. Typically, industry standards are set at about 2%-3% salt for the fish meal product. It has been proposed that electrocoagulation or hyperfiltration could be used to remove salt from the fish meal process streams without a significant removal of fish protein solids therefrom. Such prior attempts have met with limited acceptance and success. As a result of the unavailability of an effective means of removing salt from fish meal process streams, certain fish meal processing plants remove salt by sacrificing a portion of the recoverable fish meal and dumping it as a waste product. This poses at least two potential problems. First, there is the economic loss associated with the loss of the fish protein solids and fish oil present in the wasted material. Additionally, the fish protein solids in the wasted material make it more difficult to dispose of the material, particularly given the present environmental climate.